4 Questions from Geoff Forden

Geoff Forden sends along four questions that Congress should ask about the recent anti-satellite mission to destroy USA 193:

Spy Satellite Shoot-down: Four Questions for Congressional Oversight

Geoffrey Forden

Last week’s shoot-down of USA-193 appears to have eliminated whatever small chance existed of that errant satellite harming people on Earth. We will still, however, have to live with the consequences of that action for years to come. Already China and Russia have expressed concern that this was a thinly disguised test of a new space weapon. Increased transparency can minimize these consequences but it seems likely that will only come from Congressional oversight. Having spent much of my time since the shoot-down was announced trying to independently understand this anti-satellite engagement, I feel that I can make some useful suggestions to Congress about what it should ask. Here are the four most important questions Congress should try to answer:

What were the chances that the hydrazine tank would make it to the surface of the Earth intact? The White House and Pentagon were surprisingly silent on the extent of the danger this toxic substance presented to the world. The most concrete information we heard was that aerospace engineers felt that, since the tank was probably frozen after its 14 month sojourn in low Earth orbit, it stood a good chance striking the Earth intact. If we accept that, there was at most a 3.5% chance that the hydrazine would affect anyone on Earth. But just how likely was that the tank would experience a safe passage on its journey to the surface of the Earth? Even a little thought seems to indicate it was extremely slight. Besides the intense heat that would have been generated during its decent — seemingly enough to melt even a half ton of hydrazine— it would also have been subjected to enormous forces as the atmosphere slowed it down. In fact, it appears that it would have been subjected to forces fifty times its weight just caused by atmospheric braking. Resting a twenty-five ton weight on even a large ice cube should break it apart.

Why did the Pentagon shoot it down last Wednesday even though there were rough seas? It has been widely reported that the engagement cost up to $60 million dollars. It seems likely that $40 million of this was meant to be spent on collecting data about the engagement and rough seas would have degraded if not prevented much of that data from being taken. Of course, some of that money was used to determine if the hydrazine tank had been punctured, such as the spectrographic data taken by a flying observatory that looked for signs of hydrazine released into space. But most of the data would undoubtedly have contributed valuable data for improving the interceptor. It appears that the Pentagon gave up that information in order not to have a publicity disaster when reporters started asking if missile defense was only a “fair weather” defense.

Why wasn’t the tank equipped with a release valve? The United States has been put in a very awkward situation where even China, a mere year after its anti-satellite test, feels it can question our actions and motives in space. We could have avoided being placed in the very awkward position of having to choose between possibly endangering people on Earth or helping to legitimate China’s anti-satellite program by simply having a valve that would have vented the toxic gas into space if the spacecraft had not heard from its ground controllers within a month or so. This valve would probably have cost more than 50 cents but it would certainly have been worth while and it is clear that we need it on spy satellites from now on.

How much did this test contribute to legitimizing China’s anti-satellite program? Many of us who have followed this badly thought out program feel that it did. Russia and China, for instance, can point to the vast amounts of money spent of data collection as opposed to the core mission of shooting down the satellite and raise legitimate questions about our intent. Let us hear experts debate this issue in the open. Congress, by directly addressing this issue would increase the transparency of our actions and could lower their negative impact. The public would also feel that its interests were being better served if they could weigh the pros and cons of this action.

A friend of mine, who happens to be a big fan of the SM-3, writes to ask, “I want a 3 cheers for SM-3 from some people in the
media, darnit!” So, perhaps Congress, in addition to Geoff’s 4 questions, might add the one I asked a few months ago about defending NATO with the SM-3:

I don’t get it. The Aegis system is clearly the most functional of our missile defense assets, yet the MDA seems to hate it. Why?

No Responses to “4 Questions from Geoff Forden”

James | February 27, 2008

As to the last question, NIH is probably the answer. The Aegis and the SM-3 are a NAVY program, not an MDA program, which makes all the difference. Buying weapons is very rarely about military efficiency, after all.

Beyond that, one wonders why missiles defending a fixed area would need to be placed on ships at all. All this talk of counting ships is rather foolish; an attempt to prevent anyone comparing the two systems. There’s no reason the SM-3 couldn’t be fired from a land facility.

“The analysis that we’ve done is as certain as any analysis of this type can be,” said NASA administrator Michael Griffin. “The hydrazine tank will survive intact … the hydrazine in it is frozen solid. Not all of it will melt. So you will land on the ground with a tank full of slush hydrazine that would then later evaporate. The tank will have been breached — not probably, but the tank will have been breached — because the fuel lines will have been ripped out of the main spacecraft, and so that hydrazine will vent.”

So they are saying that somehow a breached tank with hydrazine venting from it’s fuel lines during a several thousand degree C re-entry will not lead to an explosion.

Hydrazine is rocket fuel and, as such, has a propensity towards explosion even at a few hundred C, especially during re-entry where (as it approaches earth) there is increasing amounts of oxidizer (a.k.a. air) present.

Furthermore, there are plasma discharges upon re-entry which would have set the keg off.

If the government did this for the benefit of humanity, its money would have been better spent, for instance, providing improved health care for wounded Iraq & Afghanistan war vets.

I would like someone in the media to launch a FOIA request to obtain the documents outlining the quantitative risk analysis of the hydrazine tank. I would be more precise than you (or Geoff) suggest above:

-what was the estimated probability of human death from the tank/hydrazine?

-what was the estimated probability of human injury from the tank/hydrazine?

One of the things we watched was the weather. We had some indications yesterday that we might have high seas, but when we actually got the ship on station, the ship reported that the seas were about two to three feet, which was well within the limits. So we had a good weather window, but what we were facing is, there is a low moving into the area, that would be in the area for the next four or five days. So we decided that we would proceed last night. The secretary made that decision, and then we moved forward.

On question #3, ISTM even with a release valve it wouldn’t have mattered because the satellite was “dead” and could not be commanded to do anything including venting the hydrazine. Even if one had been put on in an “automatic” mode, the hydrazine became frozen when the bird went dead. Then there’s the question of what effect such venting would have on the bird’s orbit, which would be uncontrolled.

Lao Tao Ren | February 27, 2008

Andy:

I disagree that a passive “automatic” release valve would not work.

When the bird re-enters, it would heat up enough to melt the hydrazine. A valve that is set at a sufficiently high pressure to prevent ‘accidental’ venting during normal orbits but set to trigger during the high temperatures expected during reentry would have done the trick. The stuff would have vented at high altitude well before the tank hit ground.

The real ‘damage’ from the shoot down is political.

Ronald Reagan | February 27, 2008

Not sure why we’re debating this. Two things should be painfully obvious to everyone:

1) This was a subtle test of our extended MDS. If you could establish a static MDS program, and couple that with a roving, difficult-to-track sea based missile shield, you can protect a lot of space and keep any ICBM-toting cowboys guessing. So why not do it? The technology is available. Announcing this to the world would be bad form, but you clearly need to push against your boundaries if you want to reach your potential, and do that via real-life tests. Consider this particular test passed.

2) This was also an attempt to portray to China and the rest of our “potential” and actual enemies that American power and military potential is limitless. Land, Air, Sea, Space, Information Technology, Nation-Building, Peace Keeping, Natural Disaster Assistance… Is there any area we don’t excel at? Most countries probably perceive the answer as “no”. Whether this is true or not is irrelevant. Its all about perception. The dollar can be weak, the economy in decline, our conventional forces pushed to the brink, a possible titanic shift in our foreign policy may be over the horizon – yet we can still hit a specific spot on a target moving at 17,000mph from a lone ship in shifting seas. We don’t even crow about it. Message sent.

I personally don’t think we should be getting into staff measuring contests with other countries, and I would say that as bad as the PR for our military has been over the past 6 years, despite overwhelming odds we have been surprisingly successful in Iraq, Afghanistan, Africa, etc. Name one other country who could have pulled off what we have accomplished? We are far from perfect, and we haven’t “won” anything, but we haven’t gone away, either. And slow as we may be, we do learn from our mistakes eventually. The military is a short term fix. Diplomacy, cultural exchange, and legitimate dialogue is the best way to keep the peace in the long term. That’s infinitely more complicated of a task than dominating in the military sphere, however. So for now, we use our military might to buy us some time while gather ourselves and begin making smarter decisions. Until that time comes, we have to reveal a big stick from time to time.

I have no doubt it’s an engineering problem that could be solved. Personally, I think a small charge of insensitive explosive attached to the tank – one that could only trigger through the heat of reentry, would do the trick by rupturing the tank on descent. Valves can be finicky things and, as noted by Yousaf, the tank would likely have been “vented” by broken fuel lines.

Geoff may want to ask a more general question, such as, “why was this eventuality not foreseen and consequently, why was the bird not engineered to consider the possibility of a full, frozen hydrazine tank deorbiting uncontrolled?”

Hmm, Russia has repeatedly paid millions of dollars for cleanup and other expenses when UDMH in the tanks of upper stages that fail and fall to Earth — undergoing significant g-forces and heating — seem somehow, despite all them there perfessers and their fancy goldarn equations, to reach the ground undispersed, and explode there, violently. Fortunately, these were in desert areas downrange of the launch sites. But is the ‘hydrazine-can’t-reach-the-ground-intact’ meme a new variation of the old classic, ‘bees-can’t-fly-because-my-equations-tell-me-so”? This is asked partially, but not entirely, in jest.

James | February 27, 2008

RR asked: “Is there any area we don’t excel at?”

Er…assessing risk in mortgage-backed securities comes to mind.

More seriously, before we get all back-slappy, it’s worth noting that this all came about because we failed to successfully deploy a critical national security asset. At the end of the day, the US needed that satellite a hell of a lot more than it needed to prove anything about missile defense.

I doubt the NRO finds the surprisingly competent performance of the SM-3 to be very much consolation for the gaping hole that now exists in its space reconnaissance program.

Allen Thomson | February 27, 2008

There’s an interesting Navy take on the future of SM-3 (presumably moving to Block II next decade) at

Regarding your Feb. 25 editorial, “Satellite fallout”: The editorial suggests that the interception of the ailing US 193 spy satellite was motivated primarily by a desire to prevent harm from its toxic fuel if the satellite fell to Earth. Whenever such operations are conducted there is a technical risk assessment done so that one can have a basis for deciding whether or not it makes sense to destroy the satellite.

Noticeably absent, in this case, were any firm numbers from the government on actual risk probabilities of the hydrazine fuel injuring anyone should it reach the ground.

In all likelihood, the risk of the satellite (or its fuel) injuring anyone was minuscule: The well-regarded Aerospace Corporation estimates that “the risk that an individual will be hit and injured is estimated to be less than one in one trillion.”

The hydrazine fuel, too, would have burned up during reentry and, in any case, its toxicity is not so high as to prevent the Air Force from transporting it by rail, sea, and even roadways.

If an arbitrary decision was made to intercept the satellite, it would be akin to robbing the United States public of about $50 million, not to mention the cost of negative international repercussions. If the decision was not arbitrary, American citizens have a right to know what the risk numbers really were of letting the satellite reenter by itself.

Yousaf Butt
Cambridge, Mass.

In response to your recent editorial on the shooting down of a US satellite: It surprises me how no one takes into consideration that this spy satellite was only launched a few years ago and contains our nation’s latest technology.

Since the larger a chunk of material is the more likely it will be to reach Earth’s surface intact, I am betting the satellite was destroyed to protect our nation’s secrets rather than to intimidate.

Allan Dennison
Acton, Mass.

Justin Case | February 28, 2008

hydrazine is an O2 scavenger used in the boilers of every steamship on the high seas.

Ya gots to be a real idiot to believe the offical story, its as absurd as the 9/11 explanation of “commanded from a cave”….

Recall that hydrazine is a liquid at standard conditions. Just opening a valve would not release it to space. Rather, what would likely happen is the hydrazine would start to boil, which would pull heat from the rest of the liquid, causing it to freeze. The same thing happens if you suddenly expose a well-insulated tank of water to vacuum: the water begins to boil, as it pulls enough heat from the remaining liquid to freeze it (I’ve done this in the lab—it’s a great and very counterintuitive demo).

For water, standard enthalpy of boiling (vaporization) is 40 kJ/mol, while the enthalpy to freeze (fusion) is only 6 kJ/mol. So, the heat you absorb in boiling to vacuum pulls enough heat to freeze much more of the remaining water to ice. The numbers for hydrazine are similar: Enthalpy of vaporization = 41.8 KJ/mol, Enthalpy of fusion = 12.6 KJ/mol.

So, by just opening a valve, you would end up in the same situation as with USA 193: a tank of frozen hydrazine.

Yousaf: “Hydrazine is rocket fuel and, as such, has a propensity towards explosion even at a few hundred C, especially during re-entry where (as it approaches earth) there is increasing amounts of oxidizer (a.k.a. air) present.”

Hydrazine vapors explode, esp. when mixed with air. Hydrazine as a liquid or solid does not.

Please, please, please, consult the industry Bible before discussing the properties or hazards of hydrazine again.

yousaf | February 28, 2008

JimO: great. get the US govt. to publish the probabilities and we will shut up.

The russian re-entries were suborbital, if downrange as you say.

Read the case of LandSat 6 and Telstar 402 and the paper cited above & tell me how a leaking tank of hydrazine survives a several thousand degree re-entry. From orbit.

Yousaf: “The russian re-entries were suborbital, if downrange as you say.”

Tanks survive reentry from orbit all the time. See this partial list, for example. Note that all the debris from upper stages (3rd stage of Delta II’s for example, which have a bad habit of dropping debris) are essentially coming in from orbit, not just down-range suborbital.

Mark Gubrud | February 28, 2008

I am not as certain as Yousaf is that the hydrazine would have melted and warmed to the point that it would have exploded inside its obviously as noncatalytic as possible containment. At some point in reentry the tank or one of its attachments would have been opened and hydrazine would have begun to vent, but whether that would have produced a violent enough explosion to destroy the tank is doubtful.

But the fact remains that, based on the “two football fields” worth of POTENTIALLY lethal contamination, should the tank have come down fully intact and full of slush hydrazine, the probability was still less than 1% (not 3.5%; humanity does not form a noninteracting 2D gas) that one or more persons would have been located within the affected area. Since they would only have been killed had they “lingered” at the site breathing the hydrazine despite the smell and burning lungs, the probability of anyone having been killed drops by another factor of ten to less than one chance in a thousand.http://www.armscontrolwonk.com/1797/usa-193-risk-calculation#comment

Since when does our government spend $50M to prevent a lethal one-time accident that has one chance in a thousand of occurring? Since it became a convenient excuse for conducting an ASAT test/demonstration.

yousaf | February 28, 2008

Andrew,
yes, I am aware of that.

When a tank of hydrazine (even if frozen — its melting point is quite high btw, like water) re-enters from orbit the heating of its thin shelled containment vessel WILL:

1. melt the outer layer of the frozen ball

2. vaporize the outermost containment vessel contact layer.

These vapors will escape from the tank and explode as they exit the broken fuel lines.

See Griffin’s quote above about broken fuel lines and breaching of the tank being a CERTAINTY.

This explosion will heat and explode the liquid and frozen ball.

BTW, this frozen business is being played WAY up — hydrazine will freeze at 1C so it is not a big deal. The satellite spent half its time in the sun so the hydrazine will NOT be at deep space temperatures.

Again, show me the probabilities of death and/or injur from the tank/hydrazine and I WILL shut up.

Yousef: “Read the case of LandSat 6 and Telstar 402 and the paper cited above & tell me how a leaking tank of hydrazine survives a several thousand degree re-entry. From orbit.”

Are you one of those people who would be astonished to discover a freshly-fallen meteorite on the ground at say 20C, gathering frost? How could that happen? How could something pass through thousands of degrees, but remain ice cold?

Or have you ever boiled water in a paper cup, over an open flame, and the paper doesn’t even char?

My point is, thermal transfer during atmospheric entry can be counter-intuitive, and I think we’ve seen examples of people getting tripped up, in recent posts.

How much of the BRIEF heat pulse on the outside of a tank gets transferred into the frozen mass of hydrazine inside? Especially since the heat of fusion for hydrazine is a whopping 395 kJ/kg.

yousaf | February 28, 2008

Andrew: & regarding your comment on Geoff’s proposal regarding the valve: You are — again — neglecting the enormous & continuous heat input due to re-entry.

Please read the plenty of AIAA papers on re-entry heating.

It is pleasant to showcase your deep knowledge of hydrazine and its phase transitions, but you have to keep in mind the larger scale engineering problem we are talking about here.

I’m not saying a valve is the best way of dealing with the problem, but your particular objection to Geoff’s proposal is not valid.

Lao Tao Ren | February 29, 2008

The point here is that a passive system that do not require ground input can be built to destroy the tank prior to it hitting ground. It may take a small explosive charge, a valve, or some other system that can keep a small staff of engineers busy.

But in order to do all that, there need to be a policy decision that such a problem is a) important enough to be dealt with, b) given a budget of resources (both on the vehicle and in terms of the overall cost / performance of the vehicle, and c) the word ‘go’ given to do it.

All of these are policy decisions – like putting passive restraint systems in cars, that do not come about without the ‘will’.

Look at the Chinese ASAT test: they could have gotten just as good validation data without the actual hit – but there has to be the will to not make a big debris cloud first.

When there is a will, there will be a way. But lets start with the will first.

Perhaps Jeffery should have phrased it as a general question as opposed to a specific method of dealing with the problem.

yousaf | February 29, 2008

Andrew,
I am well aware of tanks surviving re-entry. They don’t have hydrazine fuming from them on the ground, however.

The point is — in this case — they are saying it is the hydrazine contents that are the make or break issue.

Please re-read the background material.

Mark, the venting vaporized hydrazine WILL lead to an explosion in the several thousand degree environment, as happened in the two cases cited above.

Hydrazine has a tendency to flash back far from the original point of ignition.

Professor Oberg: I tire easily of repeating myself. Please, if you feel somehow that a leaking tank of rocket fuel can survive re-entry kindly talk to your buddies at NASA and DoD and tell them to let us know the quantitative probability levels of death/injury from the tank, and the big issue here: the hydrazine threat.

There has been a lot of speculation that the craft contains a high quantity of hydrazine rocket fuel.

“Usually, the hydrazine is consumed but I understand there could have been a malfunction, which means there is more than usual left on board,” says Dr Jehn.

“This could reduce the risk of it crashing into the Earth. When the velocity of the satellite is reduced during entry into the denser layers of the atmosphere, the satellite will get very, very hot. The hydrazine will probably cause it to explode and it will be broken up into many, many pieces.”

“We’d been practicing for a month and a half when we got told we would possibly do the mission and kept working up with a team of government experts and technicians as well as industry partners, the folks that designed the Aegis weapons system and the missile itself, and started tracking the object at different times when we could when we were underway to get radar cross-section data and that sort of thing, which was helping build the eventual program and software that we used to do it.”

“Probably the hardest part in the whole run-up to it was as it started breaking in the press we were trying to finish our training and we were on our way over to the ammo magazine to load the missiles and then proceed to sea, and I was thankful we got out to sea before it all broke.”

“We were out to sea for about a week and a half before the decision was made.”

Interesting.

Why were they practicing the interception for so long before the govt. told us that the hydrazine was a [alleged] threat?

Apparently, it was declared a threat only when they were already confident they could shoot it down.

If they couldn’t modify the codes & systems on the SM3 in time, USA-193 would have most likely burnt up harmlessly during re-entry and they may never have declared it a threat.

JimO: “Are you one of those people who would be astonished to discover a freshly-fallen meteorite on the ground at say 20C, gathering frost? How could that happen? How could something pass through thousands of degrees, but remain ice cold?”

Indeed. Even the evidence for ice meteorites reaching the ground intact is mounting, although this remains somewhat controversial. See a recent review here.

Note that a meteorite, by definition, is reentering at greater than escape velocity (11 km/s), and this represents a much, much more severe heating history than from orbit.

yousaf | February 29, 2008

OK, we may just now have an opportunity to see if they learnt their lesson regarding the hydrazine.

Now, the question is if the new spysat NROL-28 is at all similar in design to US-193 that was intercepted, then do we know — or can someone (media, NGOs, NASA…) please ask our friends at NRO — if the problem in the hydrazine tank design has been fixed, such that, if NROL-28 also does not get properly inserted into orbit that they won’t have to also use that for target practice?

Yousaf: “Mark, the venting vaporized hydrazine WILL lead to an explosion in the several thousand degree environment, as happened in the two cases cited above. Hydrazine has a tendency to flash back far from the original point of ignition.”

This is by no means clear. In fact, I think your scenario is rather unlikely.

If you recall Michael Griffin’s statement (quoted above):

“The hydrazine tank will survive intact … the hydrazine in it is frozen solid. Not all of it will melt. So you will land on the ground with a tank full of slush hydrazine that would then later evaporate. The tank will have been breached — not probably, but the tank will have been breached — because the fuel lines will have been ripped out of the main spacecraft, and so that hydrazine will vent.”

The fact that the fuel lines are open and venting hydrazine vapor makes it more likely the tank will survive reentry

Again:

—Liquid/solid hydrazine is very stable. It does not explode or detonate, even when heated. If it were not stable, it would never be used as a storable propellant.

—Hydrazine vapors can explode. We all know about the havoc cause by old Russian hydrazine tanks that explode after years on orbit. However, for the tank to explode, the hydrazine must be confined. If a tank is free to vent, it is much less likely to explode. The mechanism in these explosions is likely thermal run-away reaction. If the tank if free to vent, there is unlikely to be a build up in pressure leading to a run-away reaction (i.e., explosion). Even if the hydrazine vapors did ignite, if the tank was free to vent, it is not clear this would be sufficient to rupture the tank or ignite/initiate the frozen/liquid hydrazine.

Now, upon reentry, indeed some of the hydrazine may melt and boil, generating vapors. If the vapors are free to escape out of the ruptured fuel lines, it will likely be convected (i.e., swept) away by the hypersonic flow past the tank as it reenters. It may burn downstream, but I doubt it can “flash-back” against an oncoming hypersonic flow. The burning rate of a hydrazine/air mixture is orders of magnitude slower than the speed of the oncoming flow.

Again, I detest when it is necessary to roll out academic credentials, but I have be an active researcher in the field of detonation and explosion physics and hypervelocity flow for 20 years, and have published widely in this field (nearly 100 papers). You can see some of my publications here. Specifically, I have published papers on the detonability of hydrazine as well as combustion of volatile materials exposed to hypersonic flow. I have also consulted with NASA as a subcontractor in a 2003 study of how to design propellant tanks so that they intentionally do not survive reentry. I can provide you with references on all this material, if interested. Just e-mail me.

Based on my experience, I do not agree with your analysis and I am more in agreement with the assessment of Mike Griffin quoted above.

Yousaf: “An ESA expert — way before all the shit hit the fan — on Jan 28 completely agreed with my reasoning in a news report: ‘…The hydrazine will probably cause it to explode and it will be broken up into many, many pieces.’ ”

The expert quoted, Rüdiger Jehn, is a mathematician who works orbital mechanics, specifically in the modeling of orbital debris. I am not aware of any expertise he has in detonation/explosion physics or reentry heat transfer. He has certainly never published anything in these fields.

yousaf | February 29, 2008

Professor Oberg: the enthalpy of fusion of hydrazine is very similar to that of water…also a “whooping” 334 kJ/kg.

I am aware of this event and I’ve read the AIAA paper you cited and other papers on this issue. I believe these events have little or nothing to do with the likelihood of a freely venting tank of frozen hydrazine surviving reentry.

Opening and closing of pyrovalves can result in hydrazine vapor explosions in pressurized, confined tanks, via a number of mechanisms (waterhammer, adiabatic compression of vapors, pyrotechnic blow-by, etc.).

These are not likely to happen on reentry of a freely venting tank of frozen hydrazine.

yousaf | February 29, 2008

Andrew,
the hypersonic flow will not persist until impact (as you know).

At most the tank will be going ~200km/HOUR through the most oxidizer-rich region of the atmosphere.

Your impressive credential notwithstanding I do not find it credible that a freely venting tank of hydrazine within an oxygen-rich environment, at low speeds, heated from re-entry can possibly not ignite.

Again, it the solution to the holistic problem we are after, not a controlled experiment in a particular (hypersonic) region that is under question.

Perhaps you could get a grad student to crank out the probabilities we are after?

yousaf | February 29, 2008

Andrew,
re. LandSat 6 and TelStar 402:

The failure modes that I’ve seen published include pyrotechnic blow-by (which you also mention). This is the mode I was referring to when I made the analogy with the situation for an ignition at the fuel-line propagating to the tank — which if as is claimed to be intact is a pressure vessel, and thus confined.

Two failure modes have occurred:
(1) The burning of the valve’s titanium housing threads
allowed the initiator cartridge to be jettisoned by the
valve’s internal pressure at a velocity of over 600
feet/second, and (2) The “blowby” or venting of hot
gases and hot particles from the burning pyrotechnic
charge around the actuating piston, prior to o-ring
seating; these gases/particles entered the fluid path of
the valve, and initiated a reaction in the hydrazine,
which overpressurized and burst the system plumbing.
The first failure mode occurred in a ground test in the
European Space Agency Cluster Program. The second
failure mode, as indicated by Lockheed Martin, was
responsible for the loss of the Landsat 6 and Telstar 4.

====

So, it appears (if you trust this ref.,and Lockheed Martin) that pyrotechnic blow-by was the reason for TelStar 402 and LandSat 6 failures, and a similar failure mode can occur during the last stages of descent of the tank (i.e. non-hypersonic).

Re the question of whether the tank would freeze because it’s in sunlight half the time — the black body temp of an object at 1 AU in FULL sunlight is below 0 C. And in practice, the water tanks on Salyut-6 froze solid after several months in orbit in 1985, with power failed. The UDMH tanks did not — its freezing point is quite a bit lower.

I’m trying to argue that the heat transfer from the plasma sheath (nearly a vacuum)into the massive, frozen tank contents, would not be expected to heat much of it at all. These apparently were NASA’s results, and I’m pestering contacts to get them released.

Gubrud’s figure of 3% or less human risk is entirely reasonable to me, and in fact a 1:100 chance of casualties was the threshhold given by NASA in 2000 to terminate the Compton GRO mission while it still could perform a controlled entry.

So it seems there is a precedent for an existing threshold where active mitigation has been the national policy.

JimO: Are you one of those people who would be astonished to discover a freshly-fallen meteorite on the ground at say 20C, gathering frost? How could that happen?

It’s called “ablation”. The “freshly-fallen” meteorite was much larger before re-entry.

Teg | February 29, 2008

Guys the world is a dangerous place, sorry but that is just the reality. Minor bad guys now know, without doubt, that we CAN shoot down stuff in space – that’s a good thing. Major bad guys (China, Russia) also see that without much fuss we’ve matched and surpassed them AGAIN as far as space goes. The Chinese understand history much better then we Americans and they know that the last “super power” to engage us in an arms race lost and lost big (lesson learned). Being able to dominate space militarily is critical to our national survival… sorry I wish it wasn’t soooo but wake up guys… the Chinese are working hard to have military capability in space and they aren’t being shy about it.

Lao Tao Ren | February 29, 2008

At what point does the rhetoric on this thread hit ignition temperature for a blog?

There were no rough seas at the shoot location, or where the OI was at.

BZ on the final point, the Navy has been carrying a lot of water for those folks, and it doesn’t get highlighted enough how little they spend on AEGIS BMD.

yousaf | March 1, 2008

Andrew wrote: “Now, upon reentry, indeed some of the hydrazine may melt and boil, generating vapors. If the vapors are free to escape out of the ruptured fuel lines, it will likely be convected (i.e., swept) away by the hypersonic flow past the tank as it reenters. It may burn downstream, but I doubt it can “flash-back” against an oncoming hypersonic flow. The burning rate of a hydrazine/air mixture is orders of magnitude slower than the speed of the oncoming flow.”

You are assuming that the hydrazine in the fuel lines heated to >1000C will not auto-ignite (sans oxidizer).

This is a wrong assumption.

The hydrazine in the remnants of the plumbing off of the tank will be superheated in the re-entry heat pulse and auto-ignite. It will the flash-back to the (nearby) main tank.

You also neglect plasma discharges setting the hydrazine off. Hydrazine is sensitive to discharges.

Can you concoct a contrived situation in which the hydrazine may make it to the ground? Surely. But it is far from realistic.

HerbS. | March 1, 2008

All this “whose diploma is bigger” wanking about hydrazine is great, but it still ignores the bigger question: since when does the U.S. government spend $60M and months of planning in order to offset a very small risk to human life (not even quantifiable in terms of how many lives, nor even that the risk is fatality)? This was a military weapons exercise, done in the guise of a humanitarian operation. Oh, and it neatly ensured that the structural and systems debris (some of which is no doubt classified) would not fall intact into unfriendly hands.

yousaf | March 1, 2008

James Oberg wrote:“have you ever boiled water in a paper cup, over an open flame, and the paper doesn’t even char?”

Thank you.

This is why the heat flux during re-entry will pass mostly through the thin-shell containment vessel and serve to melt and vaporize the boundary layer of the possibly (mildly) frozen hydrazine.

Andrew wrote: “Recall that hydrazine is a liquid at standard conditions. Just opening a valve would not release it to space. Rather, what would likely happen is the hydrazine would start to boil, which would pull heat from the rest of the liquid, causing it to freeze. The same thing happens if you suddenly expose a well-insulated tank of water to vacuum: the water begins to boil, as it pulls enough heat from the remaining liquid to freeze it (I’ve done this in the lab—it’s a great and very counterintuitive demo).”

Interesting, but misses the important fact of significant heat input during re-entry.

To modify your lab demonstration to get closer the case at hand you would need to put the water in a thin shell container and then set your lab on fire, and then see what fraction of the water remains frozen.

yousaf | March 1, 2008

Geoff you make a good point I had not realised before: “Besides the intense heat that would have been generated during its decent — seemingly enough to melt even a half ton of hydrazine— it would also have been subjected to enormous forces as the atmosphere slowed it down. In fact, it appears that it would have been subjected to forces fifty times its weight just caused by atmospheric braking. Resting a twenty-five ton weight on even a large ice cube should break it apart.”

I think we can model this fairly easily; also, as the peak heat flux and peak deceleration happen close in time the innermost sphere of frozen hydrazine will smash against the containment vessel through the outer boundary layer of liquid and vapor hydrazine at 25-50g. I have not done the modeling but suspect this will pulverize the ice and more evenly distribute the heat, melting the whole block. i.e. it is not only the extra “weight” but the fact that the ice can be transported in a liquid (&vapor) medium which will lead to significant movement (at 25-50 g!!) aiding the destruction of the putative ice.

Remember, the putative hydrazine ice was not at deep space temps.

I would do the modeling but have to sail from Culebra to St. Croix on Monday (if winds co-operate) so have to get the ol’ boat ready!

Yousaf: “At most the tank will be going ~200km/HOUR through the most oxidizer-rich region of the atmosphere….I do not find it credible that a freely venting tank of hydrazine within an oxygen-rich environment, at low speeds, heated from re-entry can possibly not ignite.”

What is going to ignite the hydrazine when the tank is as slow as 200 km/hr?

You seem to believe that the tank will be residually hot due to its heating earlier in reentry. However, this is not the case. The tank will still largely be full of frozen hydrazine, which acts as an enormous thermal sink.

Allow me to lay out a scenario that is consistent with fundamental heat transfer relations and reentry physics:

The tank begins reentry nearly full of frozen hydrazine. As it reenters, it experiences intense aerodynamic heating for a period of say, 3-5 minutes. During this time, most of the heat transferred to the tank and its contents remains concentrated near the surface, since there is not sufficient time for the heat to conduct into the center of the frozen hydrazine ball. (You can estimate this depth of penetration by sqrt(alpha*time), where alpha is the thermal diffusivity of frozen hydrazine or the beryllium tank or whatever the reentry body is made of. Since alpha is of the order 10^-5 m2/s and time is 300 s, the depth of heat penetration is only a few centimeters at most.)

Now, the tank has to dissipate an enormous amount of energy during reentry, so the heat transfer will be intense. On orbit, 500 kg of hydrazine at 8 km/s has a whopping 16e9 J of energy (or 16000 MJ). Essentially, all the energy has to be dissipated into heat. However, only a tiny fraction of that energy goes into the reentry body; most of it goes into heating up the air. A very approximate dimensional analysis says that that the fraction energy that ends up in the body is given by the skin friction coefficient, Cf, which for hypersonic reentry is usually in the range 0.001 to 0.005. So, somewhere between 16 and 80 MJ of heat is going to go into the tank. This is enough heat to melt about 40 to 200 kg of hydrazine (heat of fusion = 394 kJ/kg), but not enough to melt the entire mass. Since, as I explained above, the heat will not have time to conduct into the center of the frozen hydrazine and remains concentrated at the edge, it is likely that rather than uniformly melt the hydrazine, it will melt and then significantly heat the liquid hydrazine near the periphery of the tank. Indeed, some of the hydrazine may boil.

Recall that this maximum heating is occur with the tank is still very high up (say, 30-100 km) where atmospheric pressure is very low (1 kPa down to 1 Pa). If we assume that the fuel lines leading to the tank were ruptured, then this is the same pressure inside the tank. If the rupture fuel line were pointing forward, the tank might see a higher stagnation pressure (also called pitot/dynamic/ram pressure), but the more likely scenario is the tank internal pressure is close to the ambient pressure at the altitude. At this low pressure, the hydrazine would boil easily, but the resulting vapors are at extremely low density. The hydrazine vapors are free to expand out the ruptured fuel line, so there is no build up in pressure. At this low of pressure/density, explosion of the hydrazine vapors is unlikely. It is possible that reentry heating may create a hot spot in the fuel line, for example, that could ignite the hydrazine and flash back into the tank. However, and this is a key point, even if the hydrazine ignites and burns, it is unlikely to rupture the tank. Confined gas explosions typically generate an overpressure 10 times the initial pressure (so, say 10 kPa), while the tank is designed to be pressurized to several bar, at least. So, the tank survives with frozen hydrazine still inside. Again, as I have pointed out before, frozen/liquid hydrazine is very insensitive and will not detonate.

So, now we have a robust tank that has survived reentry and any possible ignition and explosion events in the hydrazine vapors. As it continues to decelerate through the lower atmosphere and encounters higher pressure air, the heating tapers off. What is the temperature of the tank at this point? Probably very near the melt point of hydrazine (1 C), since there is still several hundred kg’s of frozen hydrazine in the tank, acting as an enormous heat sink. The temperature is certainly not greater than the boiling point of hydrazine (114 C), as any greater temperature (in the beryllium tank liner, for example) would immediately be soaked up by the phase change of the boiling hydrazine (heat of vaporization = 1300 kJ/kg at 1 atm). There is no possible ignition mechanism at this point.

Finally, the intact tank hits the ground, still more than half full of frozen hydrazine.

Just as the NASA and DOD officials stated last week.

This scenario is consistent with, and derives from, basic conservation laws, heat transfer relations, and reentry physics. While much more sophisticated analysis can be done (indeed, has been done and will be done!), I doubt the numbers here are off by more than a factor of 10.

Conclusion: Just because a statement is made by a U.S. government official does not necessarily make it wrong.

Lao Tao Ren | March 1, 2008

It is pretty clear that rhetoric on this thread has reached ignition point.

Time for the thread to be shut down.

Is there a school where participants can be sent for etiquette lessons like not writing in bold (the equivalent of all caps), etc.?

I realize that such education may be hard to come by in the colonial outposts… but…

Must be from eating too much poutines.

yousaf | March 1, 2008

Andrew,

The rupturing of the tank is not material and I was never claiming that. What I am arguing is that most/all of the hydrazine itself will be consumed due to ignition.

This is the big threat we were supposed to fear from US-193 remaining intact and re-entering by itself.

You keep saying that liquid hydrazine will not explode when in contact with ignited hydrazine vapours.

This is wrong.

Else show me a peer-reviewed publication saying that a hydrazine vapour decomposing exothermically in contact with liquid hydrazine will not set off the liquid also. You and I know how exothermic the explosive decomposition reactions are and why they will ignite the remaining liquid. i.e. raise the surface vapor pressure of the liquid such that it too is vaporised and ignited. etc. “ad infinitum” until the liquid AND in all likelihood the solid mass is melted, vapourised and ignited. I grant you that there is a small uncertainty of the initial temperature of the putative hydrazine ice, but as I argued above it is most certainly not at deep space temperatures.

So, if the hydrazine is ignited most/all of the hydrazine in the tank will have been consumed by the resulting heat, and vaporisation of the remaining liquid/solid.

I summarize the various methods that will lead to this ignition for ease of reference:

a. Due to heating of the plumbing remnants to >1000C, the exiting vapours will ignite — in the plumbing, not the hypersonic flow-field — and flash-back to set off the rest of the hydrazine.

b. Same as (a) but ignition due to plasma discharges.

II. In the non-hypersonic sonic flow (Oxidizer helps here, and there is enough at ~30-20 km altitudes)

The stagnation point heat flux will still be ~0.1 of its peak at ~30km altitude. At this point the tank will be going ~1000m/sec. The speed of sound here is ~300m/sec so we are talking Mach 3 at 30km.

By 20km the object will still be blisteringly hot as it just at the tail end of the heating profile. (It will still be heating, probably ~0.02 q/q_max or so) Here its speed will be ~500m/sec or less (Mach 1.6).

So now any hydrazine that may be leaking out will now also burn with the oxidizer outside the tank and the non-hypersonic flow-field will not suppress its flash-back.

Furthermore, we don’t know the orientation of the plumbing off of the tank and it is at least as likely that the broken fuel lines will be “force-fed” with oxidizer.

In any case, this last (II) scenario is not needed to consume the hydrazine but it’s just to show besides the cases I(a,b) there is yet another way of using up the hydrazine.

========

Lastly, as I mentioned above, as the peak heat flux and peak deceleration happen close in time the innermost sphere of putative frozen hydrazine will smash against the containment vessel through the outer boundary layer of liquid and vapor hydrazine at 25-50g, pulverizing itself (if not the vessel also). (Basically the vessel hits the putative hydrazine ice ball as it is the body being decelerated and smashes it).

I am not saying that the statement is false because a US govt official said so, but because it defies the fundamental physical chemistry of hydrazine in the re-entry scenario given the heat and electrical discharges, as well as, huge g-forces involved.

yousaf | March 1, 2008

Andrew mentioned: “It is possible that reentry heating may create a hot spot in the fuel line, for example, that could ignite the hydrazine and flash back into the tank.”

No, not only is this just possible but extremely likely. In fact, I would say impossible to avoid.

This is all I am saying.

Once the flash back occurs to the hydrazine in the tank it will vaporize the liquid there, igniting it, generating more heat, vaporizing more liquid etc. You get the picture.

I don’t really care if the tank itself survives — that happens all the time.

Conclusion: We will most likely get a empty tank on the ground — possibly ruptured from the g-forces of the internal impact with the ice ball.

Yousaf: “The hydrazine in the remnants of the plumbing off of the tank will be superheated in the re-entry heat pulse and auto-ignite. It will the flash-back to the (nearby) main tank.”

This scenario has three major flaws that make it extremely unlikely that the tank is destroyed prior to reaching the ground.

Flaw 1: Venting hydrazine will not ignite due to reentry heating. The maximum heating occurs when the ambient pressure is very, very low (1 Pa to 1 kPa). Further, while the 5000+ K plasma surrounding the reentering spacecraft sounds ferocious, it is also at these very low pressures (which are, for engineering calculations, essentially vacuum). It is very difficult to organize combustion of a gas or vapor at these low pressures. Ignition requires a critical density of energy release concentrated at one point for the reaction to continue self sustained combustion. The ignition energy (for example, the critical spark energy required for an explosion) increases extremely rapidly as pressure is lowered, roughly with the inverse-cube of pressure.

Flaw 2: Hydrazine flame/detonation will not propagate back into the tank. Neglecting Flaw 1, let’s assume that the hydrazine vapor bleeding out of a fuel line does ignite, say were it contacts the plasma sheath around the reentering tank. Can this ignition flashback into the tank? Again, the pressure in the tank is only 1 Pa to 1 kPa. For any combustible gas, there is a critical size of tube through which a flame or detonation can no longer propagate, and this critical size increases dramatically at lower pressure (the critical tube size goes up with the linear inverse of pressure). Some historical background here: this effect was first discovered with the development of the “Davy safety lamp.” In 1815, Humphry Davy discovered that if you surround a miner’s open-flame lamp with a metal screen, you can walk right through a combustible mixture without causing an explosion, because while you might ignite the gas mixture, the flame cannot propagate through the holes in the screen due to heat loss to the screen. This is something my lab at McGill does all the time: we measure the critical gap or tube size that will let a flame or detonation propagate through. This is critical information for industrial safety and handling of combustible gases, and it is the basis of flame arrestors and detonation arrestors in pipelines.

For hydrazine vapor, data on the minimum tube diameter for propagation can be found in AIAA Report SP-084-1999 Fire, Explosion, Compatibility, and Safety Hazards of Hypergols – Hydrazine. Let’s say that the fuel lines are 5 mm ID. If there is an ignition event somewhere in the line with 1 atm of hydrazine vapor, it may be possible for the ignition event to propagate into the tank as a flame or detonation, in other words, flash-back. At 20 or 50 atm pressure (where hydrazine tanks are designed to operate), an ignition even will propagate for sure. This is likely what happened on the TelStar 402 and LandSat 6 failures you cited. At 1 kPa, however, it is impossible for an event to flash-back. At pressures this low, for example, it would be necessary for the fuel line to be at least 10 cm in diameter for a detonation to propagate. At much lower pressures, it becomes impossible for a flame or detonation to propagate, even if the full volume of the tank were filled with the most sensitive mixtures (say, a stoichiometric mixture of hydrazine vapor with oxygen) and ignited.

Flaw 3: Hydrazine vapor explosion in the tank will not rupture tank. This is the major flaw in your scenario. Even if the hydrazine were to ignite and explode (neglecting Flaws 1 and 2 above), the tank will not rupture. The worst case scenario is if the ignition happened near sea level, where the vapor pressure of hydrazine could conceivably reach 1 atm. Let us also assume the worst case scenario that the tank provides perfect confinement (i.e., the rupture fuel line is so small that it cannot vent significant gas on the timescale of the explosion). The overpressure in the case of a constant volume explosion like this is about a factor of 10, giving 10 atm overpressure. This value derives from conservation of energy analysis—I can provide detailed calculations of this, if anyone is interested. So, we have the tank pressurize to 10 atm by the explosion. However, hydrazine tanks are typically designed to be pressurized to much higher pressures in operation, typically 10’s of atm. See examples here and here. These tanks have a burst pressure of 50 atm and 30 atm, respectively. So, even under the worst case scenario, the tank will survive an internal hydrazine vapor explosion intact.

This is another key difference between the uncontrolled reentry of USA 193 and the TelStar 402/LandSat 6 failures you cite (and let’s not forget Mars Observer, whose loss was also blamed on an explosion of the hydrazine tank). These events occurred in pressurized tanks or tanks that were in the process of being pressurized, already near their burst pressure (probably within a factor of 2). Any ignition/propagation event in these cases would result in the tank bursting catastrophically, for sure. But this is simply not relevant to the hydrazine tank of USA 193 reentering with a ruptured fuel line.

But couldn’t the hydrazine vapor explosion cause the frozen or slush hydrazine to explode as well? Perhaps. In my experience, however, this is very unlikely. My students and I have done quite a bit of work on this problem: Can a shock wave or explosion in a gas initiate an explosion or detonation in an explosive liquid or solid bounding it? Our findings are an overwhelming No. You can see some of our papers on this topic here and here. We even tried some very extreme things, such as shocking the air above a very sensitive explosive (PETN and aluminized PETN) to very high pressure (500 atm) and temperature (1000’s of K) and the explosives did nothing. We even recovered the explosive perfectly intact afterward; it did not even burn. The fact is that solids and liquids have 1000 times the heat capacity per unit volume and 1000’s times the impedance (stiffness) of the gas above them. This means they are simply not affected by combustion/explosion/shock waves in the gas bounding them.

All of my analysis above assumes, as Mike Griffith stated, the tank has been ripped from the spacecraft bus by aerodynamic forces early in reentry, resulting in the fuel lines leading from the tank being ruptured. We could question this scenario. However, it is consistent with the other dozen or so hydrazine tanks that have come down from orbit. The fact that the USA 193 tank was full makes it more likely it would be ripped from the bus. If you want to contest this, it is up to you to provide the analysis to show that a propellant tank can reenter while remaining perfectly sealed/confined and for the hydrazine to reach ignition conditions (in my prior posting, I provided a quantitative analysis showing that the tank likely remains cold and certainly not hotter than the boiling point of hydrazine, which is well below any autoignition condition).

Unless you provide analysis to the contrary, the best engineering assumption to make is that, like several prior tank reentries have shown, the tank will be ripped from the spacecraft bus, free to vent any hydrazine vapor building up without the risk of an explosion that could rupture the tank, and thus has a good chance of surviving reentry.

Yousaf: “Geoff you make a good point I had not realised before: ‘Besides the intense heat that would have been generated during its decent — seemingly enough to melt even a half ton of hydrazine— it would also have been subjected to enormous forces as the atmosphere slowed it down. In fact, it appears that it would have been subjected to forces fifty times its weight just caused by atmospheric braking. Resting a twenty-five ton weight on even a large ice cube should break it apart.’

I think we can model this fairly easily…”

Good idea.

As a test case of your modeling, make sure you can reproduce these results of tanks surviving reentry more or less intact.

yousaf | March 2, 2008

Andrew wrote:“What is going to ignite the hydrazine when the tank is as slow as 200 km/hr? You seem to believe that the tank will be residually hot due to its heating earlier in reentry.”

No. The most simple way for the hydrazine to ignite in the tank will be my cases 1a&b above in the hypersonic peak heat flux regime.

In the non-hypersonic regime the ignition that will have already occurred in the prior peak heat flux phase (of any residual hydrazine not auto-ignited within the fuel lines), will move from far downstream to closer and closer to the tank as:

1. The tank rapidly decelerates.

2. The amount of oxidizer increases.

(All this will be made much easier if the orientation of the fuel lies is in the direction of the velocity vector. But this is not a necessary condition.)

In any case, the main method of ignition of the hydrazine will occur around ~50-60 km height at peak heat flux with no need for oxidizer. And, as in the case of pyrotechnic blow-by of TelStar 402 and LandSat 6 this ignition will consume most/all of the hydrazine in the tank. Possibly, but not necessarily, also rupturing the tank. The latter effect will be made easier by the 25-50g impact of the putative ice ball on the thin shell vessel.

Conclusion: no hydrazine will make it to earth past, to be conservative, ~20km altitude. The tank, too, may be have been blown and/or shattered to bits.

MARGARET WARNER: Now, Professor Postol, I gather you don’t think this is a good idea.

THEODORE POSTOL, Massachusetts Institute of Technology: Well, I don’t think the idea has any technical merit. What you have is a vehicle that’s in space. It’s built as light as it possibly can be, because it’s a satellite designed to just be in space.

When this thing hits the upper atmosphere, large pieces of it are going to burn up. Now, there will be big pieces that survive to the ground, but the idea that this hydrazine tank will survive to the ground really makes no sense.

Let me just give you an example. This hydrazine tank is going to decelerate at a rate of — let me just use the numbers — 50 Gs. I just did the calculations before the program.

What that means is I take this spherical hydrazine tank and I accelerate it from rest to 1,000 miles per hour in one second. Now, this gossamer tank, this spherical tank is going to squash up and break open.

And it’s going to be — the hydrazine is going to behave like a snowball fired out of a cannon. It’s just going to spray all over the place, stop in the upper atmosphere probably at an altitude of 60 or 70 miles, and it’s never going to reach the ground.

There will be pieces of the satellite that reach the ground, but the hydrazine is never going to come close to the ground.”

My four questions for Congress to ask the Pentagon have elicited a lot of discussion; both informed and intense. I am very glad of that and hope that Congress will take the opportunity to increase the transparency surrounding the shoot-down of USA 193. The discussion has also sharpened the community’s understanding of the technical details with a very informed discussion of the heat transfer to the tank during its descent. Partially prompted by this discussion, I have gone back and re-checked my calculations of the atmospheric braking one might expect on a one meter diameter, spherical hydrazine tank and find that it is quite sensitive to the incident angle it makes with the top of the atmosphere. A more realistic value for the maximum G-forces experienced by the tank is about 10 G’s. This is probably equivalent to the forces the tank experienced during take-off and while it is possible that the tank would be subjected to these forces without the support structure provided by the surrounding satellite, it is much less clear that it would break up upon hitting the dense part of the atmosphere. (I will post the more likely force profile on our website, mit.edu/stgs, in the coming week.) Nevertheless, it is a shame that the nation is left debating these facts and trying to guess them when the government could so easily clear up all these doubts and questions if only they released more details of their calculations.

yousaf | March 2, 2008

I realised there is a case 3 also, not explored by me before:

There WILL be heating of the thin thin thin Ti shield to ~5000K during re-entry.

The hydrazine vapors this generates at the inside contact surface will auto-ignite and detonate (without any oxidizer).

If you want to average the temperatures with the putative hydrazine ice (5000+270)/2 ~ 2600K. More than enough to ignite the hydrazine vapor shell surrounding the hydrazine snowball.

Geoff: note that the ~10G upon the pressure vessel during take-off did not have a hydrazine snowball inside sitting in a shell of liquid from within which it will accelerate and likely crush itself and/or the gossamer metal shield, during re-entry.

….if it has not exploded already due to the direct heating from the re-entry thru the shell.

Lao Tao Ren: this is a fairly polite scientific exchange! ;)

I’d be happy to co-author a paper on this with Geoff/Andrew if we can agree that the hydrazine most likely will have been consumed during re-entry due to any one of my several scenarios: I(a&b), II, and III above.

I wrote: “Can a shock wave or explosion in a gas initiate an explosion or detonation in an explosive liquid or solid bounding it? Our findings are an overwhelming No. You can see some of our papers on this topic here and here.”

Ops! I had mistakenly posted the secured version of the link for one of our publications on this problem. The unsecured version is here.

Sorry for any frustration this caused.

yousaf | March 2, 2008

Andrew: your “flaws” apply only to a given orientation of the fuel lines w.r.t. the velocity vector (anti-aligned), and do not apply to my cases II, and III at all.

Yo do not discuss the effect of 10-50G on an internal snowball hitting the gossamer tank.

Lastly, for the n-th time, I do not care if the tank survives, as long as the hydrazine is used up.

This is not an argument about things you already know academically, it is a new and novel engineering problem and you ought to at least attempt to think outside the box, or the pressure vessel or whatever.

Yousaf: “There WILL be heating of the thin thin thin Ti shield to ~5000K during re-entry.”

Absolutely not. The plasma surrounding the tank will be at ~5000 K. The surface skin of the tank will not. There is a thermal boundary layer in the hypersonic flow that prevents the tank from ever contacting these temperatures.

yousaf | March 2, 2008

Andrew what will be the approximate temperature of the Ti sheath at peak heat flux?

The conclusions of my argument stand.

I hope you continued grants/contracts from NASA for your fine towing of the line.

“The tank was made of stainless steel and was protected by calcium
aluminum silicate insulation. Although ruptured at one end, the tank was in very good condition,
which was attributed to the insulation. The insulation was singed, but also was in good condition
although the predicted peak temperature was estimated to be 2,500°C. A steel collar was also
recovered and found to be in good condition.”

If we down-estimate by 1/2 for heat transfer to ice, we have a Ti sheat at ~1500K which will auto-ignite the vaporised hydrazine in the contact layer. (Like the ignition charge in a H-bomb in fact).

The subsequent heat from ignition will melt & vaporise further of the liquid and solid hydrazine snowball mass.

Yousaf: “You keep saying that liquid hydrazine will not explode when in contact with ignited hydrazine vapours. This is wrong. Else show me a peer-reviewed publication saying that a hydrazine vapour decomposing exothermically in contact with liquid hydrazine will not set off the liquid also.”

I am not aware of any studies examining liquid hydrazine specifically, however, I can recommend these studies which examine the ability of gaseous detonations (H2/O2, for example) to initiate explosives and other energetic materials that are much more sensitive and easily ignited than hydrazine, such as PETN, nitroglycerine, lead azide:

4. Tanguay, V., Mamen, J., and Higgins, A.J., “Propagation of Detonation Initiated by Precursor Shock Wave in Explosive Lined Channels,” Proceedings of the 19th International Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Kanagawa, Japan, July 27 – August 1, 2003.

In these studies (all of which underwent peer-review, except Makomaski), detonating gas above the explosive at 1 atm initial pressure did nothing to the exposed explosives. In our own studies, I can report that the explosive did not react or burn at all and the samples were recovered in pristine condition after the experiment. If you continue to increase the initial pressure in the gas/vapor reaction (to 10’s or 100’s of atm’s), you may eventually initiate the solid or liquid explosive, but never with initially atmospheric pressure. Again, most of these studies are with dry, powdered explosives which are typically orders of magnitude more sensitive and easily ignited than a homogeneous liquid like hydrazine.

In the reentry scenarios you discussed, the pressure of the hydrazine vapor will be much, much less than 1 atm. The lowest altitude you mention (corresponding to the highest altitude) is 20 km where pressure is only 5 kPa, and this will be the pressure in the tank if the fuel lines are ruptured. A hydrazine explosion at that pressure will not initiate combustion in a layer of liquid for frozen hydrazine it is in contact with.

The reason for this is due to the fact that gas at this pressure has only 1/10,000th the density (and therefore only 1/10,000th the heat capacity) of the liquid or solid it is in contact with. Even if the hydrazine vapor burns or explodes, generating 2000 K, it has a negligible ability to heat, much less ignite, a solid or liquid. This is why you can quickly pass your finger through a flame for a second or two and not even feel the heat. Your hypothethical hydrazine vapor explosion will be at lower pressure/density and will last only milliseconds. This will not result in ignition of the liquid or solid hydrazine.

Thus, the hydrazine will not be consumed on reentry via the mechanism you proposed.

Yousef: “I hope you continued grants/contracts from NASA for your fine towing of the line.”

As a player often at the full length of the tether myself, I realize there’s a fuzzy line of propriety in such a literally HEATED debate. But Yousef, I think this comment goes WAY over that line and needs a formal apology for your insulting an opponent’s motivations.

There are two factors in this interesting debate which I have not seen Mr. Higgins or Yousaf address.

First is that the hydrazine tank in USA-193 was inside a satellite. It seems to this layman that, at least for a short time, the tank would be protected by the rest of the satellite.

Secondly, there’s the difference between a full tank of hydrazine and a partially empty tank. Based on my admittedly limited knowledge of terrestrial fuel tank explosions, fuller tanks last longer than partially full ones because there is not as much explosive vapor present. I remember watching a show on a rail car tank explosion and I believe it was internal pressure from heating that eventually ruptured the tank, not an explosion itself (though the explosion happened immediately afterward as the fuel was dispersed into the air).

Do either of these factors have any meaningful effect on the discussion here?

You say that your results aren’t original. But in the context of USA
193 they are an important contribution which is not available to the
technical and policy community who are not propulsion specialists. If
they don’t warrant publication as a research paper in a propulsion
journal, I urge you to write them up for a semi-popular or general
publication – JBIS, Scientific American, J Spacecraft Rockets or
something like that.

I still believe that the risk to those on the ground, when balanced against
the debris risk and the long term international policy consequences,
did not warrant the destruction of USA 193. But you make a reasonable
case that the risk was higher than some of us had estimated.

Please confirm that I understand your assertions and assumptions correctly:

- The hydrazine used in USA 193 has a higher freezing point than the
UDMH used in Russian rockets, so the residual fuel in those rockets
(which reenter every few weeks) doesn’t freeze. The same is presumably
true for the AZ-50 hydrazine/UDMH mix used in Delta 2 rocket stages
(which also do depletion burns to avoid residuals, since the 1980s)

- If the hydrazine is frozen, the heat input during reentry is
insufficient to melt it.

- The timescale for it to evaporate in ambient air is much longer
that the timescale from reentry to impact.

- Liquid and solid hydrazine do not explode

- Some small amount of vapor must be presumably be evolved from the hydrazine during
reentry, but you think it will not cause an explosion because
it will dissipate quickly and is not pressure-confined, and any
small explosion in the tank will not rupture the tank
(but will it break up the remaining solid lump?)

- A vent valve would not have helped since it just helps the hydrazine
freeze (but a safemode which triggered a depletion burn of the thruster
presumably would work. Doesn’t the Shuttle dump extra hydrazine during
reentry? how does it do that?

- Geoff’s point about the brute aerodynamic forces on the reentering object
breaking it apart (independent of any thermal effects) seems reasonable.

I don’t think you really address that? Delta second stage reentries seem
to indicate that sometimes tanks reach the ground mostly intact, and sometimes
they break into pieces.

Jonathan McDowell: “I still believe that the risk to those on the ground, when balanced against the debris risk and the long term international policy consequences, did not warrant the destruction of USA 193.”

I agreed with you.

At the same time, I don’t think accusing DOD and NASA officials of concocting a fictional scenario to justify the incept, which many people are now doing, is very productive either.

JM: “The hydrazine used in USA 193 has a higher freezing point than the UDMH used in Russian rockets, so the residual fuel in those rockets (which reenter every few weeks) doesn’t freeze.”

Yes. Hydrazine freezes at 1 C, UDMH freezes at -57 C.

JM: “If the hydrazine is frozen, the heat input during reentry is insufficient to melt it.”

Yes. I based this off a few “best case/worst case” calculations of reentry heat transfer and the enthalpy of fusion of hydrazine.

JM: “The timescale for it to evaporate in ambient air is much longer that the timescale from reentry to impact.”

Yes, of course. Reentry is 5-10 minutes. Evaporation of half a ton of frozen hydrazine takes much, much longer.

JM: “Liquid and solid hydrazine does not explode.”

Liquid hydrazine does not detonate like a high explosive. Many people have tried this, including me but we’ve never been able to detonate it pure. It may undergo a violent and rapid decomposition that results in an explosion if it is confined, but this is technically not a detonation.

I’m not aware of any work done on frozen hydrazine, but based off my experience with other frozen energetic liquids (nitromethane, nitroglycerin, etc.), I would expect it to be more stable in frozen form.

JM: “Some small amount of vapor must be presumably be evolved from the hydrazine during reentry, but you think it will not cause an explosion because it will dissipate quickly and is not pressure-confined, and any small explosion in the tank will not rupture the tank (but will it break up the remaining solid lump?)”

Correct. I am assuming that, as Mike Griffin said prior to the intercept, that aerodynamic forces early on during reentry would rip the tank from the bus, resulting in rupture of the fuel lines. This leaves the tank free to vent any vapor to vacuum. I doubt anything could explode at these pressures (<< 1 kPa), but if it did, the tank would certainly survive. Vapor explosions only multiply initial pressure by a factor of ten, while the tank is designed to be pressurize to 10’s of bar. Thus, the tank will survive any explosion (even down to sea level pressure) if it is at ambient pressure prior to the explosion.

The hydrazine explosions that do rupture tanks (a la the old Russian upper stages on orbit) are in confined, pressurized tanks.

I doubt an explosion at these low of pressures would break up the frozen hydrazine, but even if it did, this would not affect any of the other considerations we are discussing. Also, an explosion of hydrazine vapor will not ignite the liquid/frozen hydrazine in contact with it.

JM: “A vent valve would not have helped since it just helps the hydrazine freeze (but a safemode which triggered a depletion burn of the – Geoff’s point about the brute aerodynamic forces on the reentering object breaking it apart (independent of any thermal effects) seems reasonable.”

Please note that Geoff has now corrected his calculations and the tanks would only likely see ~10 g on reentry, similar to the load they experience on lift-off.

Jonathan: “Doesn’t the Shuttle dump extra hydrazine during reentry? how does it do that?”

The shuttle cannot “dump” any propellant in the sense that an aircraft can “dump” fuel, but it does routinely “waste” leftover propellant (that had been set aside for ‘bad day’ maneuvers) during the de-orbit burn by performing that burn with an out-of-plane component. The forward RCS tanks are also depleted (the shuttle is usually ‘nose heavy’ and it’s good to move the CM as aft as possible — and forward jets, unlike aft jets, are unusable during atmospheric entry)) by firing opposing (left yaw and right yaw) thrusters (so no net vehicle torque). The problem of making this fuel depletion part of an emergency procedure, as I see it, is that the odds are a lot better the ‘pre-death dump’ routine would be triggered incorrectly, than that it would function correctly when desired. Keeping a thruster firing requires active computer control, to prevent one from starting by accident and ‘latching on’. For the shuttle, the engine-on command consists of a rapidly alternating ‘saw-tooth’ hi-low command tone that if it ever goes to constant tone, results in a thruster shutdown. This is to prevent much more likely command failures that cause a thruster to inadvertantly lock on.

The freezing point of hydrazine is about 40 degrees higher than UDMH, I believe — I can get the exact figures. It’s why the water froze on Salyut-7, but its hydrazine — UDMH — did not. Under Russian climatic conditions, using a ‘room temperature’ hypergolic propellant that froze at the average Russian room temperature for more than half the year would have been complicated — UDMH stayed liquid when it was needed to, for on-pad servicing and fuelled-stage transportation.

Ryan Crierie | March 11, 2008

To answer your question:

<B>I don’t get it. The Aegis system is clearly the most functional of our missile defense assets, yet the MDA seems to hate it. Why?</B>

It’s because the SM-3 doesn’t have sufficient delta-vee (it’s 3 km sec) at burnout; making it only good for intercepting incoming ballistic missiles within a very close range of the cruiser. It’s just not feasible to cover threat coastlines with SM-3 equipped ships.

There’s talk about CG(X) having a significantly larger VLS cell system devoted for a very long range ABM system with significantly higher delta vee.